1. Field of the Invention
The present invention relates generally to electric power distribution systems and, more particularly, to switchgear cabinetry and circuit breakers employed in power distribution systems. Specifically, the invention relates to a sealing apparatus that seals a gap between an arc hood mounted on a switchgear cabinet and a circuit breaker removably mounted in the switchgear cabinet to resist leakage of arc gases through the gap.
2. Description of the Related Art
Switchgear for electric power distribution systems includes electrical switching apparatus and their line and load terminations together with related equipment mounted in metal cabinets. Switchgear used in sections of electric power distribution systems operating at voltages up through 690 volts is classified as low voltage switchgear (according to international standards, although the ANSI standard for low voltage is a maximum of 600 volts.) Typically, the electrical switching apparatus is a circuit breaker, but other switching apparatus such as network protectors, disconnect switches, and transfer switches are also mounted in such switchgear cabinets. Henceforth, the electrical switching apparatus will be referred to as circuit breakers, although it will be understood that other types of electrical switching apparatus can be used as well.
Typically, in such low voltage switchgear, multiple circuit breakers are mounted in each cabinet in cells stacked vertically in a forward compartment. The line and load conductors are mounted in rearward compartments and engage the circuit breakers through quick disconnects as the circuit breakers are installed in the cells.
Power circuit breakers can generate significant amounts of arc gases when interrupting large currents such as those associated with a short circuit in the distribution system. It is common for the arc gases to be vented through the top or the rear of the circuit breaker. Generally, the approach is to slow the arc gases and to cool them before they leave the switchgear cabinet.
Arc gases that result from the interruption of current typically are of an extremely high velocity and are highly ionized. If such highly ionized arc gases are permitted to flow past the line conductors of the circuit breaker, such gases can promote arcing between adjacent line conductors. It is also known that similar arcing can occur between adjacent load conductors, between an outboard line or load conductor and the switchgear cabinetry, and between the quick disconnects that are connected with the line and load conductors. Henceforth, however, for the sake of simplicity all such arcing within the terminal area will be referred to as arcing between adjacent line conductors. The potential for such arcing is dependent upon the space between the adjacent conductors, the presence or absence of high dielectric insulators between the conductors, and the voltage that is delivered to the conductors, as well as the existence of arc gases and the degree of ionization thereof.
Switchgear cabinetry is thus typically designed to include one or more channels into which arc gases can be directed for dissipation thereof. In this regard, such switchgear cabinets typically include an arc hood that is mounted within each cell and is disposed above the vents in the circuit breaker through which the arc gases are exhausted.
As is known in the relevant art, circuit breakers typically are subject to a certain amount of movement during operation thereof. Moreover, circuit breakers are often slidably mounted within the cells to permit rapid removal of the circuit breakers for maintenance and for other purposes. It is desirable, therefore, that a nominal gap exist between the arc hood mounted on the switchgear cabinet and the circuit breaker to avoid interference therebetween during operation of the circuit breaker and during installation and removal of the circuit breaker into and from the switchgear cabinet.
In some applications, however, the circuit breaker is in a fixed-mount application and thus is not slidably mounted within the switchgear cabinet. Nevertheless, many of the parts employed in such applications are the same parts employed in the slidable switchgear applications, such that a gap still exists between the circuit breaker and the arc hood in fixed-mount applications.
Such a gap undesirably permits some of the arc gases to leak therethrough. Such leaking arc gases typically flow into the terminal area in the vicinity of the line conductors and increase the likelihood of arcing therebetween. It is thus preferred to provide a device and method for resisting the leakage of arc gases through such a gap between an arc hood mounted on a switchgear cabinet and a circuit breaker mounted on the switchgear cabinet. Such a device and method preferably would improve the ratings of the circuit breaker.
This need and others are satisfied by the invention which is directed generally to a seal apparatus that spans a gap between an arc hood mounted on a switchgear cabinet and a circuit breaker moveably carried on the switchgear cabinet. The seal apparatus includes a seal member mounted on the arc hood with a plurality of fasteners. The circuit breaker is movable between a racked position within a cell of the switchgear cabinet and an unracked position external to the cell. When the circuit breaker is in the racked position, the arc hood is disposed adjacent the circuit breaker, and the seal member sealingly extends across a gap between the arc hood and the circuit breaker to resist the flow of arc gases through the gap. The seal apparatus thus resists the direct flow of arc gases into the region of the line conductors at the rear of the circuit breaker. The seal member is advantageously received against and elastically deflected by the circuit breaker in the racked position.
An objective of the present invention is to provide a power distribution system that resists arc gases from directly flowing into contact with line conductors on the circuit breakers.
Another objective of the present invention is to provide a seal apparatus that can improve the performance ratings of a power distribution system.
Another objective of the present invention is to provide a seal apparatus that resists the flow of arc gases directly toward the line conductors on the circuit breakers.
Another objective of the present invention is to provide a seal apparatus that can be retrofitted onto existing switchgear cabinetry.
Another objective of the present invention is to provide a seal apparatus that promotes the flow of arc gases in a desirable discharge direction while permitting a gap to exist between an arc hood on a switchgear cabinet and a circuit breaker within the switchgear cabinet.
Another objective of the present invention is to provide a flexible seal that permits a circuit breaker to be racked into and out of a switchgear cabinet without causing damage to or diminishing operation of the circuit breaker or the switchgear cabinet.
An aspect of the present invention thus is to provide a power distribution system, the general nature of which can be stated as including a switchgear cabinet having an arc hood, a circuit breaker movably carried on the switchgear cabinet, the circuit breaker being movable along a longitudinal axis between a racked position and an unracked position, and a seal apparatus mounted on one of the circuit breaker and the switchgear cabinet, the arc hood being disposed at least partially adjacent the circuit breaker when the circuit breaker is in the racked position, the arc hood being structured to direct arc gases in a discharge direction, the seal apparatus sealingly extending between at least a portion of the arc hood and at least a portion of the circuit breaker when the circuit breaker is in the racked position, the seal apparatus being structured to resist the flow of arc gases in a leakage direction.
Another aspect of the present invention is to provide a seal apparatus for resisting the flow of arc gases through a gap between a circuit breaker and an arc hood in a switchgear cabinet, the general nature of which can be stated as including a seal member mounted on one of the arc hood and the circuit breaker and structured to sealingly extend along at least a portion of the gap between the arc hood and the circuit breaker.
Still another aspect of the present invention is to provide a method of resisting the flow of a quantity of arc gases through a gap between an arc hood mounted on a switchgear cabinet and a circuit breaker movably mounted on the cabinet, the general nature of which can be stated as including the steps of mounting a seal apparatus on one of the switchgear cabinet and the circuit breaker and sealingly spanning the seal apparatus across at least a portion of the gap.